Keep the proxy app fast with many flows

The app held every flow in memory and redid all of its work for each new
one: the sidebar mounted every domain and path node (its tree scrolled
inside a container that never bounded it), every tree row looked up its
atoms by scanning every atom the family had made, and the layout, detail
pane and list rows re-rendered per flow. At 3,000 flows each new one cost
about 90 ms of main thread, more than the traffic left time for.

The app now holds a window of the newest 2,000 flows, applies new ones in
batches, and loads older ones in pages from the database on scrolling to
the top, through a new list_flows RPC that pages in SQL. The database
keeps every flow.

Also adds clear_flows: an RPC, POST /flows/clear on the control API, and
a Clear button in the header that Cmd+K opens, confirming first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package-lock.json

@@ -249,7 +249,6 @@
         "@tanstack/react-virtual": "^3.14.17",
         "@tauri-apps/api": "^2.12.3",
         "@tauri-apps/plugin-os": "^2.4.0",
-        "@yaakapp-internal/model-store": "^1.0.0",
         "@yaakapp-internal/proxy-lib": "^1.0.0",
         "@yaakapp-internal/theme": "^1.0.0",
         "@yaakapp-internal/ui": "^1.0.0",